Ethylene polymerization in nonionic emulsion systems



United States Patent 3,226,352 ETHYLENE POLYMERIZATIQN IN NONTONICEMULSION SYSTEMS Arthur F. Helin and Gerald ll. Mantel], Kansas City,Mo., assignors to Gulf Oil Corporation, Pittsburgh, Pa, a. corporationof Pennsylvania No Drawing. Continuation of application Ser. No. 44,862,July 25, 1960. This application Dec. 24, 1964, Ser. No. 421,100

6 Claims. (Cl. 260-29.6)

This application is a continuation of our copending application, S.N.44,862, filed July 25, 1960, now abandoned.

This invention relates to emulsions of polymeric materials. Moreparticularly, this invention is concerned with novel stable aqueousnonionic emulsions of polyethylene, processes of producing the same, andnovel polyethylene products.

Polyethylene finds many important uses because of its desirable physicaland chemical properties. Included within such uses is the employment ofpolyethylene as a surface coating. The polyethylene is applied tosurfaces in several ways including extrusion, gluing and in the form ofemulsions. Polyethylene emulsions heretofore available have not beenespecially satisfactory because of poor stability, difiiculty inmanufacture and low solids content.

According to the present invention there are provided novel polyethyleneemulsions in water characterized by good stability and which areodorless, colorless, milky, low viscosity liquids.

The novel polyethylene emulsions of this invention are produced bypolymerizing ethylene in an aqueous medium under suitable polymerizationinducing temperatures and pressures with a polymerization initiator andin the presence of a nonionic alkylphenoxy polyoxyethylene ethanolemulsifier of the formula wherein R is an alkyl chain having 8 or 9carbons, advisably branched such as a polypropylene or polybutylenechain and n represents an average of 7 to about 15. Surprisingly, manyother emulsifiers which were tried, including similar structures, didnot Work at all or gave emulsions of low solid content or partialstability.

Some of the emulsifiers that can be used in the process are Triton X-100of the formula Triton X-114 of the formula Triton N-101 of the formulaTriton N-128 of the formula Tergito-l NPX of the formula and I-gepalCO730 of the formula 0 nmQ-o-w m-cnz-o 13. 11

The amount of emulsifier included in the reaction mixture is notnarrowly critical but will depend somewhat upon the extent to which thepolymerization is carried, viz., the amount of polyethylene formed.Thus, more emulsifier should be employed when the polymerization isconducted to produce an emulsion of 20 to 25% solids content than whenthe solids content is say 15 to 20% Irrespective of the extent of thepolymerization, however, an amount of emulsifier is advisably used toconstitute about 5 to 20%, and advisably, 10 to 15%, by weight of thesolids content in the resulting latex or emulsion. In general, aboutl to5% weight of emulsifier based upon the weight of liquid medium can beused for the polymerization.

Although the polymerization can be readily effected in the presence ofwater as the sole liquid medium, it is advisable to include an alcoholsuch as t-butanol therein. Such aqueous-alcoholic medium can contain anyamount of an alcohol of a type which favorably influences thepolymerization and the resulting emulsion. Thus, up to about 35% byweight, based on the combined weight of alcohol and water, of an alcoholsuch as t-butanol can be acceptably included in the polymerizationmedium with about 7 to 25% by weight being most suitable.

The polymerization is conveniently elfected at temperatures of about 60to 150 C., with a temperature in the range of to 120 C. advisably used.Presently, the preferred initiation temperature is less than about 100C. and advisably about C., with the polymerization then being completedat a higher temperature such as about 120 C. or above. Pressures fromabout 2000 psi. to 20,000 p.s.i. and higher can be used; however,pressures of about 2500 to 4500 psi. are particularly suitable forproducing the emulsions. It is to be understood, however, thatparticular temperature-pressure relationships are to be used which givethe desired stable aqueous latex and not conditions which might pervertthis objective.

Conventional polymerization initiators of the watersoluble persulfateclass such as alkali metal persulfates including potassium or sodiumpersulfate and other watersoluble persulfates, e.g., ammoniumpersulfates and the like can be used. Generally from 0.08% to 0.50% byweight of initiator based on the liquid reaction medium is adequate forthe polymerization.

The polymerization can be effected batchwise. In a batchwise operation,the liquid reaction medium is added to an autoclave together with thenonionic emulsifier. The autoclave is advisably equipped with a stirreror agitator. After purging the autoclave, such as with ethylene, thecharge is heated to the polymerization temperature and then the ethylenepressure is raised to that to be used for the polymerization. While themixture is agitated a solution of the initiator in water is pumped in.As the polymerization proceeds, additional ethylene is continuously fedin to maintain the pressure. The polymerization is permitted to proceeduntil the emulsion reaches the desired solids content. This can bedetermined by periodically withdrawing samples from the autoclave as thepolymerization progresses. The polymerization is generally sufficientlyfar along in about 2 to 5 hours to yield an emulsion of the desiredsolids content. The emulsion produced directly in the polymerizationshould generally have a minimum of about 14% solids by weight forpractical reasons but usually not over 25% solids by weight since higherconcentrations lead to emulsions of lowered stability and prefioc orunemulsified polyethylene. A latex with a solids content of about 17 to22% is considered best. In any event the polymerization advisably shouldbe terminated when the total solids contain about to 15% by weight ofthe nonionic emulsifier. The polymer particle size will usually be ofthe range of 0.03 to 0.15 microns.

Following the polymerization any solvent present such as t-butanol canbe stripped from the latex and the latex concentrated by distillationunder reduced pressure until the solids content is up to 30 to 50%,without adverse effect on the stability of the emulsion.

The polyethylene resin can be isolated from the emulsion by suitablecoagulating techniques such as by the use of isopropanol containing asmall amount of concentrated hydrochloric acid. The precipitated polymercan be filtered and washed with isopropanol and water. The polyethyleneso obtained will generally have a density of at least 0.928 and asoftening point above 100 C.

It has been found that the novel emulsions produced according to thisinvention contain novel modified polyethylene resins comprising theemulsifier linked chemically to polyethylene chains. It is believed thatthe emulsifier functions to a limited extent as a chain transfer agentWith emulsifier radicals forming end groups on polyethylene chains. Thepresence of the polyethylene-emulsifier resin is established byconcentrating an emulsion produced according to this invention todryness and repeatedly extracting the solids, as with methanol, ethanoland then hexane. Thus, an emulsion containing solids having 16% TritonN-lOl (on solids) lost 14.4% (on solids) of the emulsifier uponextraction with methanol but after leaching with ethanol and n-hexanethe polyethylene contained 0.74% Triton N101. This was after a totalextraction time of 370 hours. Solution and reprecipitation of thepolyethylene did not remove the emulsifier. The amount of emulsifiercombined with polyethylene is considerably higher than that presentafter the ethanol and n-hexane extractions because these solventsextract low molecular weight polyethylene as well as the emulsifier.

In general, up to about 3 to 4% by weight of the total solids in theemulsion usually constitutes emulsifier bonded to polyethylene chainsalthough the amount will, of course, vary according to the extent towhich the polymerization is carried and the amount of emulsifier used.The emulsifier modified polyethylene resin will usually constitute about20 to by weight of the total solids content.

The novel emulsions provided by this invention form adherent, tough,glossy films on paper (HO-120 C.) which have good moisture vapor barrierproperties. Thin films on smooth surfaces are hard, tough, glossy,adherent, non-smearing coatings. The emulsions are useful in textilefinishing, polishes, printing inks, surface coatings, as for example,paints and industrial finishes.

The following examples are presented to illustrate the invention.

Example 1 To a mixture of 72 lbs. of distilled water and 13.5 lbs. oft-butanol was added 2.7 lbs. of Triton N-101 in a 15 gallon mixing tank.The stirred mixture was pumped into an 18 gallon autoclave equipped withtwo 5-inch propeller-type agitators. The autoclave was purged withethylene (agitator off) and the charge was heated to C. with theagitator rotating at 654 r.p.m. Ethylene supplied from a compressor waspumped in until the pressure reached 2500 p.s.i.g. At this time aninitiator solution containing 0.22 lb. of potassium persulfate in 4.5lbs. of distilled water was pumped into the autoclave. The ethylenepressure was adjusted to 3000 p.s.i.g. and maintained there by anautomatic control system. During the course of 4 /2 hours small sampleswere removed eriodically and solids content determined. The ethylenefeed was discontinued when the solids content reached 17.4%. The productwas discharged into a receiving vessel at atmospheric pressure. Theproduct was a smooth, white latex of uniform consistency containing noundispersed solid polymer. The latex pH was 2.5. The particle size wasapproximately 0.05 to 0.1 microns as determined by an electronmicrograph.

Part of the product was stripped of butanol and concentrated in a22-liter rotating flask at reduced pressure in a heated bath. The finaltotal solids content was 41.8%. Little or no separation of solidsoccurred during these operations. The concentrated latex was stable toacids, bases, polyvalent metal cations and vigorous mechanicalagitation.

A portion of the unstripped latex was coagulated by addition to threetimes its volume of isopropanol containing 1.6% by volume ofconcentrated hydrochloric acid. The mixture was heated to 60 C., cooledand filtered with suction. The filter cake was reslurried in a volume ofdistilled water equal to 84% of the isopropanol used in the first stepand refiltered. The pressed filter cake was dried in a vacuum oven at 50C. The polymer thus isolated was a white powder having the followingproperties:

Inherent viscosity (0.1 g. in 50 cc. of tetralin at Melt index475 at C.

Density0.93

Ring and ball softening point105106 C.

An infrared spectrum of a molded film had absorption bands at 6.2, 6.6and 9.0 microns corresponding to bands present in Triton Nl01. Thesebands were not removed by extraction with boiling methanol for 15minutes or at room temperature for 69.5 hours, thus demonstrating thatthe Triton N-101 combined with the polymer to the extent of 3% by weightof the product.

Exam ple 2 To 1600 g. of Water was added 57 -g. of Triton X305 (70%active) and to this solution was added 300 g. of t-butanol. The solutionwas placed in a l-gallon Magne Dash autoclave which was sealed,evacuated, purged twice with ethylene at 200 lb./ sq. in. and filledwith ethylene to a pressure of 1000 lb./sq. in. The agitator was startedand the temperature was increased to 80 C. A solution of 3.8 g. ofpotassium persulfate in 76.2 g. of water was added and the pressure wasadjusted to 3000 lb./sq. in. After /2 hour, 0.95 g. of potassiumpersulfate in 19 g. of Water was added and this was repeated at 2 hoursand at 2 /2 hours. After 5 hours the reaction was terminated. Theproduct remaining was a white latex containing 19.1% total solids.

Example 3 A 60 g. portion of Triton X-100 was dissolved in 1600 g. ofwater and 300 g. of t-butanol was added. The solution was placed in al-gallon Magne Dash autoclave which was sealed, evacuated, purged twicewith ethylene at 200 lb./sq. in. and filled with ethylene to a pressureof 1000 lb./sq. in. The agitator was started and the vessel was heatedto 80 C. A solution of 3.8 g. of potassium persulfate in 76.2 g. ofWater was added and the pressure was adjusted to 3000 lb./sq. in. Afterabout 1 hour a solution of 0.95 g. of potassium persulfate in 19 g. ofwater was added and this was repeated at 3 /2, 4 /2, 5 /2 Example 4 An80 gram portion of Triton X-100 was dissolved in 1900 g. of distilledwater and the solution was placed in a l-gallon Magne-Dash autoclave.The autoclave was sealed, evacuated and purged by flushing twice withethylene at 200 lb./ sq. in. and filled with ethylene to a pressure of900 lb./ sq. in. The agitator was started and the temperature was raisedto 100 C. A solution of 4.8 g. of potassium persulfate in 95.2 g. ofwater was added and the pressure was adjusted to 4500 lb./sq. in. After2%. hrs., 1.2 g. of potassium persulfate in 23.8 g. of water was added.Ethylene was added as required to maintain 4200-4500 lb./sq. in.pressure. After 6% hours the reaction was terminated. The product was awhite latex containing 13.7% total solids.

xample 5 A 60 g. portion of Triton X-114 was added to 1600 g. ofdistilled water and 300 g. of t-butanol was added to this solution. Thesolution was placed in a l-gallon Magne Dash autoclave which was sealed,evacuated, purged twice with ethylene at 200 lb./sq. in. and filled withethylene to a pressure of 1000 lb./ sq. in. The agitator was started andthe temperature was increased to 80 C. A solution of 4.8 g. of potassiumpersulfate in 95.2 g. of water was added and the pressure was adjustedto 3000 lb./sq. in. After /2 hour, 1.2 g. of potassium persulfatedissolved in 23.8 g. of water was added and this was repeated at 4, 6.3,and 7.1 hours. After 8 hours the reaction was terminated. The productwas a white latex containing 14.8% total solids. The latex was strippedof butanol and concentrated to 22.5% total solids by vacuumdistillation. The polymer isolated from this latex had an inherentviscosity of 0.725 with some insoluble material present and a density of0.9327 g./ml.

Example 6 A 60 g. portion of Tergitol NPX was added to 1600 g. ofdistilled water and 300 g. of t-butanol was added to the solution. Thesolution was placed in a l-gallon Magne Dash autoclave which was sealed,evacuated, purged twice with ethylene at 200 lb./sq. in. and filled withethylene to a pressure of 1000 lb./sq. in. The agitator was started andthe vessel was heated to 80 C. A solution of 4.8 g. of potassiumpersulfate in 95.2 g. of water was added and the pressure was adjustedto 3000 lb./sq. in. After 1 hour, 1.2 g. of potassium persulfatedissolved in 23.8 g. of water was added and this was repeated at 5.4hours and 7.3 hours. After 8 hours the reaction was terminated. Theproduct was a latex containing 17.0% total solids. A large amount ofprefloc was present in the reactor. The weight of the washed and driedprefloc was 122 g. The polymerization was obviously carried beyond thepoint where there was sufiicient emulsifier present to stabilize thepolymer.

Example 7 A 60 g. portion of Igepal CO-730 was dissolved in 1600 g. ofdistilled water and 300 g. of t-butanol was added. The solution wasplaced in a l-gallon Magne Dash autoclave which was sealed, evacuated,purged twice with ethylene at 200 lb./sq. in. and filled with ethyleneto a pressure of 1000 lb./sq. in. The agitator was started and thevessel was heated to 80 C. A solution of 4.8 g. of potassium persulfatein 95.2 g. of water was added and the pressure was adjusted to 3000lb./sq. in. After 5.2 hours the reaction was terminated. The product wasa smooth white latex containing 15.3% total solids. A portion of thelatex was stripped of butanol and concentrated to 22.4% total solids byvacuum distillation. The polymer isolated from this latex had aninherent viscosity of 0.716, a melt index of 460, a density of 0.9421and a melting point of 99103 C.

Example 8 Final Total Solids, percent Parts Reaction t- Time, butanolHr.

Polymerization Rate Parts/hr.

Polymer Inherent Viscosity Run These results show that the reactionrate, as well as the molecular weight of the polymer, go up as theamount of t-butanol is raised.

Various changes and modifications of the invention can be made and, tothe extent that such variations incorporate the spirit of thisinvention, they are intended to be included wihin the scope of theappended claims.

We claim:

1. The method of preparing a stable aqueous emulsion of polyethylene inone step comprising polymerizing ethylene in an aqueous mediumcontaining dissolved therein a water soluble persulfate polymerizationinitiator and an emulsifying agent consisting essentially of a non-ioniccompound of the formula wherein R represents an alkyl group having 8 to9 carbon atoms and wherein n is an average number of from 7 to 15, saidresulting emulsion comprising:

(a) a continuous aqueous phase; (b) said non-ionic compound and (c) aplurality of polyethylene particles, at least a portion of thepolyethylene in said particles being modified by chemical combinationwith said non-ionic compound. 2. Method of claim 1 wherein saidinitiator is an alkali metal persulfate.

3. Method of claim 1 wherein said non-ionic compound 4. Method of claim1 in which t-butanol is present in said aqueous medium.

5. The method of preparing a stable aqueous emulsion of polyethylene inone step comprising intimately contacting ethylene with from 0.08 to0.50% by weight of a water soluble alkali metal persulfatepolymerization initiator, said initiator being dissolved in an aqueousmedium consisting essentially of water, about 7 to 25% by weight oft-butanol and about 1 to 5% by weight of a non-ionic compound of theformula wherein R represents an alkyl group having 8 to 9 carbon atomsand wherein n is an average number of from 7 to 15, said contactingbeing carried out with agitation at a pressure of about 2,000 to 20,000p.s.i. and a temperature of about 60 to 150 C. until the solids contentof said emulsion is about 15 to 25% by Weight of the emulsion, saidresulting emulsion comprising:

(a) a continuous aqueous phase; (b) said non-ionic compound; and (c) aplurality of polyethylene particles, at least a portion of thepolyethylene in said particles being modified by chemical combinationWith said non-ionic compound. 6. A method of claim 5 wherein saidemulsion is thereafter stripped of t-butanol and Water to yield anemulsion product containing up to about 50 weight percent solids.

References Cited by the Examiner UNITED STATES PATENTS 2,449,489 9/1948Larson 26029.6 2,592,526 4/1952 Seed 26094.9 2,728,755 12/1955 Weiseman26029.6

MURRAY TILLMAN, Primary Examiner.

N. F. OBLON, Assistant Examiner.

1. THE METHOD OF PREPARING A STABLE AQUEOUS EMULSION OF POLYETHYLENE INONE STEP COMPRISING POLYMERIZING ETHYLENE IN AN AQUEOUS MEDIUMCONTAINING DISSOLVED THEREIN A WATER SOLUBLE PERSULFATE POLYMERIZATIONINITIATOR AND AN EMULSIFYING AGENT CONSISTING ESSENTIALLY OF A NON-IONICCOMPOUND OF THE FORMULA